The air cylinder is a structure which controls air pressure by using the piston's stretch out and draw back and has characteristics of accepting accumulation of pressures and automatically returning after removing external forces due to the compressibility of air pressure. Thus, it is applicable in a lot of living goods such as trunk of the car, automatic door closer, and sports equipment, and apparently an extremely broad range of applications in the market.
The air cylinder is also applied to prosthesis joint and used as medical device providing cushioning function as an alternative of joint. In the common design of the prosthesis joint, the functional purpose is realized mainly by filling the cylinder with air having a predetermined pressure and then cooperating with the operation of the piston rod.
The air needs to be filled and adjusted to reach particular pressure value before the assembly, while after a period of use, the air pressure in the air cylinder body will be gradually leaked, which further leads to lack of air resistance and the defect that the cushioning effect is reduced.
On the other hand, in order to guide the circulation of the internal air, the air cylinder requires additional air flow channel structure, which increases the production complexity and the weight of air cylinder.
In conclusion, the traditional cushioning air cylinder seals the air in the inner of the cylinder body to circulate, which usually requires complex mechanism to reduce the leaking speed of the air; however the defect of air leakage under long-term use has not been overcome yet, the users still have to endure the trouble of repairing and readjustment, and are unable to feel substantial convenience and adequacy.